Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Question: How has European settlement of Eastern North America modified tree species assemblages?. Location: The northern temperate forests of the Lower St. Lawrence region (Quebec, Canada).

Methods: Changes in relative prevalence of tree taxa were reconstructed with early land survey records (1821–1900) and modern forest inventories (1980–2010). Forest composition reconstructions were then used to analyse changes in tree taxa assemblages at the landscape scale and test for potential landscape homogenization.

Results: Our results show important maple (Acer saccharum and A. rubrum) and poplar (Populus tremuloides and P. balsamifera) encroachment, shifting from the 6th to the 2nd position of relative prevalence and from the 7th to the 5th position, respectively, resulting in a significant shift in tree assemblage. Maple has spread throughout the whole landscape and tended to become the most abundant taxon in communities where they were already present in pre-settlement times. Poplar also widely spread throughout the landscape but rarely became the most abundant taxon. Accordingly, deciduous encroachment clearly engendered a spatial homogenization of composition at the landscape scale.

Conclusion: Considering that both red maple and trembling aspen are opportunist early-successional species, the increased relative prevalence of both species, as well as the consequent reorganization of tree taxon assemblages and landscape homogenization, probably resulted from the regional convergence toward an early-successional state. Along with the restoration of long-lived shade-tolerant conifer populations, land and forest managers should aim to increase the heterogeneity of forest stand composition to improve forests resilience to future global changes.